chrome.bluetooth: respect the characteristic's writeWithoutResponse property
chrome.bluetooth: respect the characteristic's writeWithoutResponse property

Without this, writes to a device I'm testing fail.  Responses are
provided through characteristic changed notifications.

pwnall/cordova-plugin-chrome-apps-bluetooth,MobileChromeApps/cordova-plugin-chrome-apps-bluetooth,pwnall/cordova-plugin-chrome-apps-bluetooth,MobileChromeApps/cordova-plugin-chrome-apps-bluetooth